<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <!DOCTYPE html>
    <html>
      <head>
        <meta charset="UTF-8">
        <title>网页计算器</title>
      </head>
      <body>
        <p>整数1：<input id="num1" type="text"></p>
        <p>整数2：<input id="num2" type="text"></p>
        <p>
          <input type="button" value="相加" onclick="calc(add)">
          <input type="button" value="相减" onclick="calc(sub)">
          <input type="button" value="相乘" onclick="calc(mul)">
          <input type="button" value="相除" onclick="calc(div)">
        </p>
        <p>结果：<input id="result" type="text" readonly></p>
        <script>
          function calc(func) {
            var result = document.getElementById('result');
            var num1 = parseInt(document.getElementById('num1').value);
            var num2 = parseInt(document.getElementById('num2').value);
            if (isNaN(num1) || isNaN(num2)) {
              alert('请输入数字');
              return false;
            }
            result.value = func(num1, num2);
          }
          function add(num1, num2) {    // 加法
            return num1 + num2;
          }
          function sub(num1, num2) {    // 减法
            return num1 - num2;
          }
          function mul(num1, num2) {    // 乘法
            return num1 * num2;
          }
          function div(num1, num2) {    // 除法
            if (num2 === 0) {
              alert('除数不能为0');
              return '';
            }
            return num1 / num2;
          }
        </script>
      </body>
    </html>